Skid control system for automotive vehicles

ABSTRACT

A skid control system for automotive vehicles having hydraulic brakes includes a wheel speed detector and a memory circuit connected to the detector to store the initial speed of the vehicle at the start of braking. A pressure detecting means is connected to the brake system to detect the fluid pressure during brake application, and a function generator converts the detected pressure into an arbitary function proportional thereto, and which is integrated. The integrated function is compared to the stored initial speed of the vehicle to derive a difference value which is amplified and supplied to a comparator connected to the wheel speed detector to provide a control signal. This control signal operates a servo mechanism to control the braking system in accordance with the control signal.

llnited States Patent 1191 Ochia 1 1 Fell). 27, 1 973 SKID CONTROLSYSTEM FOR 3,413,456 11/1968 Sutton ..235/l97 X AUTOMOTIVE VEHICLES3,401,984 9/1968 Williams et al......

3,467,443 9/1969 Okamoto et al. ..303/21 BE Inventor: Takeshl Ochm, y hAlchl- 3,443,082 5/1969 Abe ..235 197 ken, Japan 3,523,195 8/1970 Thomaset a]. ..235/l97 X [73] Assigneez i g i Kogyo Kabushiki PrimaryExaminer-Milton Buchler Kals Ale Japan Assistant ExaminerStephen G.Kunin [22] Filed: June 30, 1970 Attorney-McGlew and Toren [21] Appl.N0.: 51,117 [57] ABSTRACT A skid control system for automotive vehicleshaving [30] Forelgn Apphcaho" Pnomy Data hydraulic brakes includes awheel speed detector and July 1,1969 Japan ..44 51477 a memory circuitconnected to the detector to Store the initial speed of the vehicle atthe start of braking. 52 s CL 303/21 A 1 1 1 C 235/197 A pressuredetecting means 18 connected 10 the brake 303/21 307/229 system todetect the fluid pressure during brake appli- 51 Int. Cl. ..l 360t 8/08and a function general cmwms the detected 58 Field of Search Lina/39515- 188/181 235/197- Pgessure 3 arbtary 5 g? g f t ereto, an w ic isintegrate e integrate uncq 303/20 307/118 328/142 40/229 tion iscompared to the stored initial speed of the vehi- 5 6 R t Ct d cle toderive a difference value which is amplified and I 1 e erences l esupplied to a comparator connected to the wheel UNITED STATES PATENTSspeed detector to provide a control signal. This control signal operatesa servo mechanism to control the 3,493,682 1970 Mueller 6! brakingsystem in accordance with the control signal. 3,433,536 3/1969 Skinner3,506,810 4/ 1970 Katell ..235/197 X 5 Claims, 6 Drawing Figures r 1WHEEL EED SWITCH MEMORY CIRCIUT OF DETECTOR INITIAL SPEED Vw 5b 6 (V0) 71 l sus- BRAKE PRESSURE FUNCTION INTEG- M TRACTOR DETECTOR GENERATORRATOR (P) 1191 .ffl lol I {9 MP E'IER A Ll r- CONTROLLER vOMPARATOR R cU T {Vw-V(l- {VG- 1v=vo- 11p1dn VPAIENTEIJFEBZYIQB SHEET PRIOR ART SPEEDD ETECTO R SWITCH MEMORY CIRCIUT OF INITIAL SPEED DECELERATION DETECTORSUB- INTEG- TRACTOR RATOR fadt 8 (Vs) CONTROLLER COMPARATOR AMPLIFIERCIRCIUT DETECTOR SWITCH MEMORY CIRCIUT OF INITIAL SPEED PRESSUREDETECTOR FUNCTIO GENERATOR SUB- I N TEG- TRACTOR RATOR H ft(P)dt 8CONTROLLER COMPARATOR AMPLIFIER CIRCIUT INVENTOR.

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BRAKE OIL PRESSURE P SKID CONTROL SYSTEM FOR AUTOMOTIVE VEHICLESBACKGROUND OF THE INVENTION When a travelling automotive vehicle isbraked hard, as during an emergency stop, the wheels are locked andslide over the road surface due to the inertia of the vehicle. Thisincreases the stopping distance for the vehicle and also results in lossof control and directional stability of the vehicle. The result of thisis the so-called skid phenonmenon, which results in a hazardous ordangerous situation. In order to prevent the occurrence of a skidphenomenon, various skid control systems have been proposed to bring avehicle to a stop in a minimum stopping distance and without locking thewheels.

A typical example of a prior art skid control system is illustrated inFIG. 1, wherein a speed detector 2, such as a DC generator, is coupledto a wheel 1 either directly or through a gear or belt transmission. Thespeed detector generates a voltage Vw proportional to the peripheralspeed of wheel 1. A switch connects speed detector or controller 2 to amemory circuit 4, and disconnects memory circuit 4 from detector 2 uponinitiation of braking and, at the same time, supplies an operationstarting signal to an integrator 6. Memory circuit 4 memorizes theperipheral velocity of wheel 1 at the time of brake application, as aninitial speed Vo.

A deceleration detector 5 detects acceleration or deceleration of thevehicle by positional deviation of a weight supported by, for example, aspring, the deviation being measured from a rest position of the weightat a time when acceleration-or deceleration is zero. The decelerationdetector converts the deviation to an electrical quantity. Integrator 6integrates the output of a of a deceleration detector 5 from the startof brake application.

A subtractor 7 is connected to memory circuits 4 and to integrator 6,and subtracts the output aadt of integrator 6 from the output V0,representing the initial speed, from memory circuit 4. An amplifier 8amplifies the output Vs of subtractor 7 by a constant coefficient (l 8).A comparator 9 is connected to the output of amplifier 8 and to speeddetector 2 and compares the output Vs of speed detector 2 with theoutput Vs(l 8) of amplifier 8, and supplies a control signal to acontroller 10, such as a servo mechanism, which controls the applicationof hydraulic brakes 11 when the output of speed detector 2 is greaterthan that of amplifier 8, but releases the brakes when the output ofspeed detector 2 is less than the output of amplifier 8.

In the system shown in FIG. 1, memory circuit 4 memorizes the peripheralvelocity Vo of wheel I at the instant the brakes are applied to wheel 1.Since, at this time, wheel 1 is rotating and not sliding, the storedvalue Vo can be regarded as the actual vehicle velocity 0 surface andwith the tire conditions. When the relation between the peripheralvelocity of wheel 1 and the actual vehicle velocity is Vw (l -().2)=0.8V, a desirable braking is obtained with a minimum stopping distanceand without skidding of the vehicle. In other words, if theamplification ratio of amplifier 8 is set at 0.8, the amplifier outputprovides the desirable peripheral velocity of wheel 1 during braking.

However, the system shown in FIG. I has the disadvantage that the use ofa gravity type deceleration detector results in errors depending on thegrade of a road surface or the attitude of the vehicle, resulting in theimpossibility of obtaining a high degree of control.

SUMMARY OF THE INVENTION This invention relates to a skid control systemfor automotive vehicles, such as automobiles, and more particularly to anovel and improved skid control system whose operation is independent ofthe grade of the road or the attitude of the vehicle.

The invention skid control system is based upon the relation between thepressure in a hydraulic brake system, during braking, and thedeceleration of a vehicle, also during braking. Taking note of thisrelation, the present invention provides a skid control system of highaccuracy and at a lower cost by utilizing, instead of a decelerationdetector, which is sensitive to the grade of a road surface and to theattitude of a vehicle, a hydraulic brake system pressure detector and afunction generator constantly connected to the pressure detector.

An object of the invention is to provide an improved skid control systemfor automotive vehicles.

Another object of the invention is to provide such a skid control systemwhich has a high accuracy.

A further object of the invention to provide such a skid control systemwhich is inexpensive and reliable.

Another object of the invention is to provide such a skid control systemwhich is insensitive to the grade of a road surface and to the attitudeof a vehicle.

A further object of the invention is to provide such a skid controlsystem including a pressure detector for the fluid pressure in ahydraulic brake system and a function generator connected to thepressure detector.

For an understanding of the principles of the invention, reference ismade to the following description of a typical embodiment thereof asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings:

FIG. 1 is a block diagram of a conventional prior art skid controlsystem;

FIG. 2 is a block diagram of a skid control system embodying theinvention;

FIG. 3 is a graphic illustration of the relation between the oilpressure in a brake system, the

deceleration of a vehicle and the slip ratio when the oil pressure isamplified linearly;

FIG. 4 is a graphic illustration of the performance of the skid controlsystem embodying the invention;

FIG. 5 is a schematic wiring diagram of a function generator formingpart of the invention skid control system; and

FIG. 6 is a graphic illustration of the characteristic of the functiongenerator shown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 2 through 6,which illustrate a preferred embodiment of the present invention, thecomponents of the skid control system shown in FIG. 2 are the same asthose shown in FIG. 1 with some exceptions, and consequently parts ofFIG. 2, which are identical with the same parts of FIG. 1, have beenindicated by the same reference numerals. One of the differences betweenthe system shown in FIG. 2 and that shown in FIG. 1 is that thedeceleration detector 5 of FIG. 1 is replaced by a pressure detector 5a,such as a distortion pressure gauge which detects, as an electricalsignal, the pressure of the hydraulic fluid in the brake system. Afunction generator 511 is connected to the output of pressure detector5a and converts that output to a value proportional to the decelerationof the vehicle. This function is obtained or derived as a result ofexperiments on vehicles.

An example of the function will now be described with reference to FIG.3, in which the abscissae represent the pressure P of the fluid in thebrake system 11, and the ordinates represent the deceleration a and theslip ratio 6. Curves A and A represent the deceleration and the slipratio, respectively, of a vehicle on a high friction road surface.Curves B and B represent these values on a low friction road surface.

As will be clear from FIG. 3, when the slip ratio 6 is less thanapproximately 0.2, the relation between the fluid pressure P of thebrake system and the deceleration a is linear, and therefore therelation 01 KP, wherein K is a constant, is established. Accordingly, inthis case, the deceleration a is readily obtained by multiplying theoutput P of pressure detector 5 by K, using the function generator 5b.

The relation between the peripheral velocity or speed of wheel 1 and theactual vehicle velocity is graphically illustrated in FIG. 4, whereinthe abscissae represent the time and the ordinates represent the wheelvelocity and the fluid pressure in the brake system. The actual vehiclevelocity is indicated by the curve V. The curves Vw and V(l 8) representthe peripheral velocity of wheel I, and that of wheel I when rotatedwith a slip 8, respectively, when the frictional braking torque is at amaximum. The curve P represents the time variation of the brakingpressure.

Usually, the peripheral velocity Vw of wheel 1 during travel of thevehicle is equal to the actual velocity V at times in advance of thestarting time t1 of the brake application. When brake application isstarted at time :1, the peripheral velocity Vw at this time is stored asthe braking initial speed V0 in memory circuit 4. The actual vehiclevelocity, obtained by substracting the integrated value o'adt of thedeceleration a from the initial speed V0 will become V. The peripheralvelocity of wheel I, V(l 5)=V( 1-0.2), which is obtained by multiplyingthe actual vehicle velocity by the slip 5, for example, O.2, is based onthe maximum frictional braking force. At the start of braking, theperipheral velocity Vw is, of course, greater than V(1 8), and thereforebraking is maintained. At the point t2 where the wheel starts todecelerate due to sliding and the value Vw becomes smaller than V(I 8),a brake releasing signal is derived from comparator 9, by means of whichthe braking is released without the fluid pressure in the braking systembeing suddenly reduced to zero. At the point t3 where the value Vwbecomes greater than V, a braking signal is again delivered fromcomparator 9 to again brake the wheels. By the repetition of thesesteps, the vehicle is gradually decelerated.

As previously mentioned, the present invention obviates the use of theinertia of a weight, as required in conventional skid controlarrangements, and therefore highly accurate braking control is effectedwithout being influenced by the attitude of a vehicle, the grade of aroad surface, or the roughness of a road surface. Additionally, apressure detector can be manufactured at a lower cost than theconventional gravity influenced deceleration detectors, and hasexcellent durability without being influenced by vertical vibrations ortemperature changes.

If function generator 5b is constructed to have a nonlinearcharacteristic rather than a linear characteristic, a control of higheraccuracy can be effected. When the brakes are applied, the loaddistribution on the front and rear wheels is changed due todeceleration. Thus, the load on the front wheels is increased and thaton the rear wheels is decreased, compared to the respective loadingswithout brake application. The larger is the frictional coefficient ofthe road surface, the greater is the deceleration, and accordingly thegreater is the load variation. For example, if a speed detector isinstalled on the rear wheel to control braking, the variation in load onthe rear wheel is small under a low braking pressure and smalldeceleration on a slippery road surface, and thus the relation betweenthe braking pressure and the deceleration can be linear. On the otherhand, on a non-slippery road surface, the load of the vehicle at thefront wheels becomes greater due to a high braking pressure and agreater acceleration, while the load at the rear wheel is decreased. Inthis case, skidding is likely to occur at a lower brake pressure than inthe case where no load variation is caused.

If the change in deceleration in relation to the output of the pressuredetector is not greater than the linear function, the response to theactual deceleration becomes inaccurate, because the output of thepressure detector has a value lower than the required value. If therange'between them is changed in the nth power (n I), the responsebetween the brake pressure and the deceleration becomes accurate. Incases when the control is effected by detecting the rotation of the rearwheel, a function generator should be designed so that an nth powerfunction is obtained at a high pressure rather than at a lower pressure.In the case of a front wheel speed detection, the nth power functionshould be obtained at a low pressure rather than at a higher pressure.

FIG. 5 is a wiring diagram illustrating a function generator Sb usedwith rear wheel speed detection. For

this function generator, a conventional polygonal line approximationfunction generator, for use with an analog computer, is utilized. Avoltage proportional to the braking pressure P is applied to inputterminal 18 of the function generator 5b and is amplified within thefunction generator to provide an output voltage proportional to p"(n gl) is derived from output terminal 19. The anodes of diodes 30, 31 and32 are connected to input terminal 18 through respective resistances 20,21 and 22 of different ohmic values. The cathodes of these diodes arecommonly connected to a negative input terminal ofa first amplifier 40.Diodes 30, 31 and 32 are biased, in the reverse direction, from aterminal 17 through respective resistances 23, 24 and 25 of differentohmic values. The positive input terminal of amplifier 40 if grounded,and a feedback resistance 26 is connected between the output ofamplifier 40 and its negative input terminal.

The output terminal of amplifier 40 is connected, through a resistance27, to a negative input terminal of a second amplifier 41 whose positiveinput terminal is grounded. The output terminal of amplifier 41 alsoserves as the output terminal 19 of function generator 5b. A feedbackresistance 28 is connected between the output terminal of amplifier 41and its negative input terminal. By means of the function generatorshown in FIG. 5, an arbitrary deceleration curve, approximated by thepolygonal line, in relation to pressure P is obtained as shown in FIG.6. It is also possible to effect brake control in the same manner asdescribed above by detecting the braking force applied during brakingindirectly through measurement of the distortion of a wheel shaft or awheel shaft bearing, instead of detecting the pressure in the brakingsystem. In this case, a correction due to load variation on the wheel isalso necessary. As mentioned above, a skid control system of higheraccuracy can be obtained employing a nonlinear function generator.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. An automotive vehicle skid control system for a vehicle having pluralwheels including front wheels and rear wheels, with at least one wheelbeing controlled, comprising, in combination, fluid pressure operatedwheel brake applying means; speed detecting means operable to detect thespeed of at least one wheel of the vehicle; memory means operativelyconnected to said speed detecting means to store the initial speed ofthe vehicle at the start of brake application; pressure detecting meansconnected to said brake applying means to detect the fluid pressureduring brake application;

non-linear function generating means connected to said pressuredetecting means and operable to convert the value of the detected fluidpressure into a nonlinear functional value related to deceleration;integrating means connected to said function generating means; derivingmeans connected to said memory means and to said integrating means andderiving the difference between said initial speed and the integratedvalue; amplifying means connected to said deriving means and operable tomultiply the output of said deriving means by a factor dependent uponthe slip of the wheel on a road surface; comparator means connected tosaid amplifying means and to said detecting means and operable tocompare the output of said amplifying means with that of said speeddetecting means; and servo mechanism connected to said comparator meansand to said brake applying means and operable to control operation ofthe latter in accordance with the output of said comparator.

2. An automotive vehicle skid control system, as claimed in claim 1, inwhich said deriving means comprises a subtractor connected to saidmemory means and to said integrating means.

3. An automotive vehicle skid control system, as claimed in claim 1, inwhich said function generating means has an input terminal, an outputterminal and a third terminal; plural diodes having their anodesconnected to said input terminal through respective resistances ofdifferent ohmic values; a first amplifier having a negative inputterminal commonly connected to the cathodes of said diodes; respectiveresistances, of different ohmic values, connected to said third terminaland biasing said diodes in the reverse direction; said first amplifierhaving a grounded positive input terminal; a feedback resistanceconnecting the output terminal of said first amplifier to its negativeinput terminal; and means connecting the output terminal of said firstamplifier to the output terminal of said function generating means.

4. An automotive vehicle skid control system, as claimed in claim 3, inwhich said last named means comprises a second amplifier having anegative input terminal connected to the output terminal of said firstamplifier through a resistance, and having a grounded input terminal;means connecting the output terminal of said second amplifier to theoutput terminal of said function generating means; and a second feedbackresistance connecting the output terminal of said second amplifier tothe negative input terminal thereof.

5. An automotive vehicle skid control system, as claimed in claim 4, inwhich the characteristic curve of said function generating meanscomprises a series of interconnected straight lines extending at anglesto each other.

1. An automotive vehicle skid control system for a vehicle having pluralwheels including front wheels and rear wheels, with at least one wheelbeing controlled, comprising, in combination, fluid pressure operatedwheel brake applying means; speed detecting means operable to detect thespeed of at least one wheel of the vehicle; memory means operativelyconnected to said speed detecting means to store the initial speed ofthe vehicle at the start of brake application; pressure detecting meansconnected to said brake applying means to detect the fluid pressureduring brake application; non-linear function generating means connectedto said pressure detecting means and operable to convert the value ofthe detected fluid pressure into a nonlinear functional value related todeceleration; integrating means connected to said function generatingmeans; deriving means connected to said memory means and to saidintegrating means and deriving the difference between said initial speedand the integrated value; amplifying means connected to said derivingmeans and operable to multiply the output of said deriving means by afactor dependent upon the slip of the wheel on a road surface;comparator means connected to said amplifying means and to saiddetecting means and operable to compare the output of said amplifyingmeans with that of said speed detecting means; and servo mechanismconnected to said comparator means and to said brake applying means andoperable to control operation of the latter in accordance with theoutput of said comparator.
 2. An automotive vehicle skid control system,as claimed in claim 1, in which said deriving means comprises asubtractor connected to said memory means and to said integrating means.3. An automotive vehicle skid control system, as claimed in claim 1, inwhich said function generating means has an input terminal, an outputterminal and a third terminal; plural diodes having their anodesconnected to said input terminal through respective resistances ofdifferent ohmic values; a first amplifier having a negative inputterminal commonly connected to the cathodes of said diodes; respectiveresistances, of different ohmic values, connected to said thIrd terminaland biasing said diodes in the reverse direction; said first amplifierhaving a grounded positive input terminal; a feedback resistanceconnecting the output terminal of said first amplifier to its negativeinput terminal; and means connecting the output terminal of said firstamplifier to the output terminal of said function generating means. 4.An automotive vehicle skid control system, as claimed in claim 3, inwhich said last named means comprises a second amplifier having anegative input terminal connected to the output terminal of said firstamplifier through a resistance, and having a grounded input terminal;means connecting the output terminal of said second amplifier to theoutput terminal of said function generating means; and a second feedbackresistance connecting the output terminal of said second amplifier tothe negative input terminal thereof.
 5. An automotive vehicle skidcontrol system, as claimed in claim 4, in which the characteristic curveof said function generating means comprises a series of interconnectedstraight lines extending at angles to each other.